Typical patient monitoring systems and some other medical instruments and systems measure different physiological values, and, thus, can provide measurements of ECG, respiration, SpO2, blood pressure etc. If a detected physiological parameter exceeds or under-runs a preset limit an alarm is generated.
However, in order to avoid nuisance alarms it is known to use an alarm delay between the event of exceeding or under-running a preset limit and the actual generation of the alarm. Such an alarm delay is often a compromise between warning the clinical staff fast enough about a change in the patient's condition on the one hand and generation of too many unjustified and, thus, nuisance alarms which detract the clinical staff from other work, especially more important alarms, on the other hand.
From U.S. Pat. No. 5,865,736 a method and apparatus for nuisance alarm reduction are known. There, it is described that when a detected value for a physiological parameter passes a threshold, both the amount of time in which the measured value has passed the threshold and the amount by which the threshold is passed are determined. Then a combination of the amount of time and of how much the measured value has passed the threshold, especially as an integral or some function of an integral, is calculated. An alarm is only generated, if the combination of the amount of time and of how much the measured value has passed the threshold exceeds a predefined threshold. However, with this method and apparatus nuisance alarms cannot be sufficiently avoided because the integral continues to increase as long as the measured physiological value is above the threshold, even if the amount of how much the threshold is passed is decreasing, i.e. the patient's condition is improving.